Back to EveryPatent.com
| United States Patent |
5,655,311
|
|
Affa
|
August 12, 1997
|
Position measuring device
Abstract
A position measuring device for measuring the relative position of a first
object and a second object. The position measuring device having a support
body having a measuring representation, wherein the support body is
attached to the first object by a translatory seating. A scanning device
that scans the measuring representation along a measuring direction X,
wherein the scanning device is attached to the second object. The
translatory seating having an elastic adhesive layer extending in the
measuring direction (X) and positioned between the support body and the
first object so that a translatory distance compensation between the
support body and the first object is made possible.
| Inventors:
|
Affa; Alfred (Stein/Traun, DE)
|
| Assignee:
|
Dr. Johannes Heidenhain GmbH (Traunreut, DE)
|
| Appl. No.:
|
397434 |
| Filed:
|
March 1, 1995 |
Foreign Application Priority Data
| Mar 02, 1994[DE] | 44 06 799.2 |
| Current U.S. Class: |
33/706; 33/702 |
| Intern'l Class: |
G01B 011/04 |
| Field of Search: |
33/700,702,703,704,706,707,708
|
References Cited
U.S. Patent Documents
| 4198757 | Apr., 1980 | Nelle et al. | 33/706.
|
| 4320578 | Mar., 1982 | Ernst | 33/706.
|
| 4492033 | Jan., 1985 | Ichikawa | 33/706.
|
| 4586760 | May., 1986 | Welker.
| |
| 4776098 | Oct., 1988 | Nelle | 33/702.
|
| 4912856 | Apr., 1990 | Ernst | 33/702.
|
| 5065525 | Nov., 1991 | Szenger | 33/702.
|
| 5115573 | May., 1992 | Rieder et al. | 33/707.
|
| 5157846 | Oct., 1992 | Fromme | 33/704.
|
| 5375338 | Dec., 1994 | Nelle | 33/702.
|
| Foreign Patent Documents |
| 0 110 059 | Oct., 1983 | EP.
| |
| 0 264 801 | Oct., 1987 | EP.
| |
| 294563 | Dec., 1988 | EP | 33/702.
|
| 025 05 587 | Aug., 1976 | DE.
| |
| 35 09 390 | Nov., 1985 | DE.
| |
Other References
Patent Abstracts of Japan, P-493, vol. 10/No. 256, Sep. 2, 1986.
|
Primary Examiner: Bennett; G. Bradley
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Claims
I claim:
1. A position measuring device that measures the relative position of a
first object and a second object, said position measuring device
comprising:
a support body having a scale located in a housing, wherein said support
body is attached to said first object by a translatory seating;
a scanning device that scans said scale along a measuring direction X, said
scanning device is attached to said second object; and
wherein said translatory seating comprises an elastic adhesive layer
extending in the measuring direction (X) and positioned between said
support body and said first object to provide translatory distance
compensation between said support body and said first object.
2. The position measuring device of claim 1, wherein said support body has
a plurality of end pieces and said elastic adhesive layer is positioned
between at least one end piece of said support body and said first object.
3. The position measuring device of claim 1, further comprising a first
fastening element that is rigidly fastened to said first object, said
first fastening element is fastened to said support body with the
interposition of said elastic adhesive layer.
4. The position measuring device of claim 2, further comprising a first
fastening element that is rigidly fastened to said first object, said
first fastening element is fastened to said support body with the
interposition of said elastic adhesive layer.
5. The position measuring device of claim 3, wherein
said support body comprising a groove or a projection which extends in the
measuring direction X; and
said elastic adhesive layer is placed between at least one surface of said
groove or projection extending in the measuring direction X and a surface
of said first fastening element so that said first fastening element is
fastened with a degree of translatory freedom.
6. The position measuring device of claim 4, wherein
said support body comprising a groove or a projection which extends in the
measuring direction X; and
said elastic adhesive layer is placed between at least one surface of said
groove or projection extending in the measuring direction X and a surface
of said first fastening element so that said first fastening element is
fastened with a degree of translatory freedom.
7. The position measuring device of claim 3, wherein said first fastening
element is a rail extending along the measuring direction X.
8. The position measuring device of claim 5, wherein said first fastening
element is a rail extending along the measuring direction X.
9. The position measuring device of claim 3, wherein a second fastening
element that extends in the measuring direction X and is spaced apart from
said first fastening element is provided.
10. The position measuring device of claim 5, wherein a second fastening
element that extends in the measuring direction X and is spaced apart from
said first fastening element is provided.
11. The position measuring device of claim 5, wherein said groove or
projection has an undercut.
12. The position measuring device of claim 6, wherein said groove or
projection has an undercut.
13. The position measuring device of claim 5, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a surface of said first fastening
element and said casting compound.
14. The position measuring device of claim 5, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a lateral surface of said groove
or projection and said casting compound.
15. The position measuring device of claim 8, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a surface of said first fastening
element and said casting compound.
16. The position measuring device of claim 8, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a lateral surface of said groove
or projection and said casting compound.
17. The position measuring device of claim 11, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a surface of said first fastening
element and said casting compound.
18. The position measuring device of claim 11, wherein said first fastening
element and a lateral surface of said groove or projection define a gap
extending in the measuring direction X, said gap is filled with a
relatively inelastically curing casting compound; and
said elastic layer is positioned between a lateral surface of said groove
or projection and said casting compound.
19. The position measuring device of claim 13, comprising an additional
sliding layer provided between said elastic layer and said casting
compound.
20. The position measuring device of claim 13, comprising a sliding layer
provided between said elastic layer and said lateral surface of said
groove or projection.
21. The position measuring device of claim 13, comprising a sliding layer
provided between said elastic layer and said lateral surface of said
fastening element.
22. The position measuring device of claim 17, wherein said gap is covered
by a sealing element.
23. The position measuring device of claim 1, further comprising an elastic
attachment device to fasten said scale to said support body.
24. The position measuring device in accordance with claim 23, wherein said
elastic attachment device comprises an elastic adhesive layer interposed
between said scale and said support body.
25. The position measuring device of claim 1, wherein said support body is
additionally rigidly fastened to said first object at approximately its
center.
26. The position measuring device of claim 1, wherein said support body
comprises a housing with a hollow chamber to which said scale is fastened.
27. A position measuring device that measures the relative position of a
first object and a second object, said position measuring device
comprising:
a housing having a scale located in the housing, wherein said housing is
attached to said first object by a translatory sealing;
a scanning device that scans said scale along a measuring direction X, said
scanning device is attached to said second object, wherein said
translatory sealing comprises an elastic adhesive layer extending in the
measuring direction X and positioned between said housing and said first
object to provide translatory distance compensation between said housing
and said first object; and
a first fastening element that is rigidly fastened to said first object,
said first fastening element is fastened to said housing with the
interposition of said elastic adhesive layer.
28. The position measuring device of claim 27, further comprising an
elastic attachment device to fasten the scale to said housing.
29. A position measuring device that measures the relative position of a
first object and a second object, said position measuring device
comprising:
a housing having a scale located in the housing, wherein said housing is
attached to said first object by a translatory seating;
a scanning device that scans said scale along a measuring direction X, said
scanning device is attached to said second object; and
wherein said translatory seating comprises an elastic adhesive layer
extending in the measuring direction (X) and positioned between said
housing and said first object to provide translatory distance compensation
between said housing and said first object.
30. The position measuring device of claim 29, wherein said housing has a
plurality of end pieces and said elastic adhesive layer is positioned
between at least one end piece of said housing and said first object.
Description
POSITION MEASURING DEVICE
Applicant claims, under 35 U.S.C. .sctn.119, the benefit of priority of the
filing date of Mar. 2, 1994, of a German application, copy attached, Ser.
No. P 44 06 799.2, filed on the aforementioned date, the entire contents
of which are incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a position measuring device for measuring the
relative position of two objects. A support body with a measuring
representation is fastened to a first object which is scanned by a
scanning device. The scanning device is fastened to the other object,
wherein a translatory distance compensation between the support body and
the first object is made possible.
BACKGROUND OF THE INVENTION
Such position measuring devices are employed for measuring the relative
position of two components of a machine tool or a coordinate measuring
machine.
A linear measuring device is known from German Patent Publication DE 25 05
587 C3, wherein the ends of a graduation support are suitably fastened to
one of the components by hinge-like embodied fastening elements.
A similarly designed linear measuring device is described in European
Patent Publication EP 0 110 059 B1. Elastic fastening means are provided
on the ends and a rigid fastening element in the center of the housing.
Fastening is done by means of a highly elastic adhesive layer in order to
additionally prevent measuring inaccuracies in case of different
coefficients Of expansion between the measurement representation and the
support body.
In accordance with European Patent Publication EP 0 264 801 A1, the
measurement representation is seated on spheres for linear compensation.
The linear measuring device in accordance with German Patent Publication DE
35 09 390 A1--on which the instant invention is based--has elastic
fastening elements at the ends of the housing and further fastening
elements located between them. These further fastening elements are
fastening elbows which are clamped to the housing by means of sliding
blocks engaging a groove. Elastic intermediate layers are intended to
allow a translatory movement between the housing and the fastening elbows.
However, it is disadvantageous that a tension-free connection cannot be
made because of the screw fastening. It is impossible in actuality to
tighten the screws with the sliding blocks evenly, so that different
forces act on the housing at the individual fastening locations, which in
turn can result in measurement errors.
In view of the above-review of the state of the art, it is an object of the
present invention to provide a position measuring device wherein uneven
thermal properties of the support body and the object to be measured and
on which the support body is fastened cannot practically cause any
falsification of the measured results.
It is another object of the present invention to provide a support body
which is fastened relatively free of tension, yet which is stable.
Another object of the present invention is to provide simple and
space-saving fastening.
SUMMARY OF THE INVENTION
The present invention regards a position measuring device for measuring the
relative position of a first object and a second object. The position
measuring device has a support body having a measuring representation,
wherein the support body is attached to the first object by a translatory
seating. A scanning device that scans the measuring representation along a
measuring direction X, wherein the scanning device is attached to the
second object. The translatory seating has an elastic adhesive layer
extending in the measuring direction (X) and positioned between the
support body and the first object so that a translatory distance
compensation between the support body and the first object is made
possible.
The present invention provides an advantage in that an almost unimpeded
linear expansion between the support body and the object to be measured
can take place.
Another advantage of the present invention is that stable and
oscillation-free fastening is assured.
Another advantage of the present invention is that it provides a simple and
space-saving construction.
Examples of the present invention will be described in detail by means of
the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cut-away view of an embodiment of a linear measuring
device according to the present invention;
FIG. 2 shows a cross section through the linear measuring device of FIG. 1
taken along the line II--II;
FIG. 3 is a further cross section through the linear measuring device of
FIG. 1 taken along the line III--III;
FIGS. 4 to 13 show cross-sectional views of ten embodiments of fastenings
to be used with a linear measuring device according to the present
invention;
FIG. 14 shows an embodiment of a separate fastening element according to
the present invention;
FIGS. 15 to 18 show various embodiments of end pieces to be used with a
linear measuring device according to the present invention; and
FIGS. 19 to 22 show further embodiments of linear measuring devices
according to the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
An encapsulated linear position measuring device for measuring the relative
position between two objects is shown in FIG. 1. The measuring device has
housing 1 constituting a support body having measurement representation or
scale 2, with graduation 3 applied thereto. Measurement representation 2
is photoelectrically scanned along a measuring direction X by scanning
device 4. Housing 1 is a hollow chamber made of aluminum, in whose
interior measurement representation 2 made of glass is fastened. Housing 1
is attached to object 5 and scanning device 4 is attached via fixture 7 to
the other object 6 to measure the relative movement between the two
objects 5, 6. For example, one object may be carriage 5 and the other
object may be bed 6 of a machine tool.
Measurement representation 2 is attached to an interior surface of housing
1 by means of an elastic attachment device, such as elastic adhesive layer
8, which is interposed between measuring representation 2 and housing 1.
The elastic attachment device causes the translatory seating or expansion
of measurement representation 2 in response to temperature changes to be
uniform along the entire measurement length. Thus, an increase in the
ambient temperature results in measurement representation 2 expanding
uniformly in all directions, starting at the center M.
A fastening element, such as rail 9 which is made of steel, is provided for
fastening housing 1 to a surface of carriage 5 via a translatory seating.
It is already known from German Patent Publication DE 23 49 944 C3 and
U.S. Pat. No. 4,586,760 to fasten the housing via a rail. With these known
linear measuring devices the connection between the housing and the rail
is made by means of screws, because of which distortions of the housing
occur and no free linear expansion between the rail and the housing is
possible in case of temperature changes. In contrast to this, in
accordance with the present invention a translatory seating is provided
which is rigidly fastened to carriage 5 via a highly elastic adhesive
layer 10 extending in the measuring direction X. Elastic adhesive layer 10
is interposed or positioned between housing 1 and carriage 5 so that a
translatory distance compensation between housing 1 and carriage 5 is
possible.
Rail 9 is glued onto a projection or into groove 11 of housing 1 which
extends over the entire length of housing 1 along the measuring direction
X. Preferably this is accomplished by placing elastic adhesive layer 10
between at least one surface of the projection or groove 11 that extends
in the measuring direction X and a surface of rail 9 so that rail 9 is
fastened with a degree of translatory freedom.
As shown in FIGS. 2-3, rail 9 and the lateral surface of the projection or
groove 11 of housing 1 define a gap extending in the measuring direction
X. In order to make the connection between housing 1 and carriage 5
especially stable and oscillation-free, a relatively solidly or
inelastically curing casting compound 12 and adhesive layer 10 are
inserted in the gap. Casting compound 12 is inserted in the gap between
adhesive layer 10 on the lateral surfaces of rail 9 and the lateral
surfaces of the projection or groove 11. Adhesive layer 10 has a
continuously even thickness of approximately 0.1 mm, which assures the
same properties over the entire housing length. Rail 9 is securely screwed
to carriage 5 by means of screws 13 and 14. To obtain a stable reference
mark for measurement in the center M of housing 1, screw 15 is disposed at
this location M, by means of which housing 1 is rigidly connected with
rail 9 and, thus, rigidly with carriage 5. This connection is shown in
detail in FIG. 3. With a small and therefore lightweight housing 1, screw
15 can be omitted and replaced by a connection shown in FIG. 2. In this
case a measurement reference point necessarily results in the center M of
housing 1, from which housing 1 can expand symmetrically in the measuring
direction X during temperature changes.
As shown in FIGS. 2 and 3, housing 1 is supported on a surface of carriage
5 to further increase the oscillation resistance. A further adhesive layer
16 is provided on this support surface A and is covered by a sliding
surface 17 resting on the surface of carriage 5. By means of this step the
unhampered linear expansion between housing 1 and carriage 5 is also
assured on the support surface A. It is also possible to apply another
elastic layer to support surface A. Also, only one adhesive layer can be
provided on the support surface A.
In the following examples in accordance with FIG. 4 to FIG. 9, rail 9 is
embodied to be dovetailed, instead of rectangular as in FIGS. 2-3, which
improves the interlocking between housing 1 and rail 9. In the embodiments
of FIGS. 4-9, the projection or groove 11 housing 1 is undercut to
resemble the shape of rail 9. Furthermore, rail 9 and the lateral surface
of the projection or groove 11 of housing 1 define a gap extending in the
measuring direction X. It is understood that other groove or projection
shapes with undercuts are also conceivable.
In FIG. 4, rail 9 is fixed in place by adhesive layer 10 on the bottom of
the dovetail-shaped groove 11 of housing 1. Casting compound 12 is applied
directly to the two surfaces of groove 11 that face each other. Adhesive
layer 10 is then applied to the lateral faces of the rail and acts as a
separating layer between the rail and casting compound 12. Rail 9 is
fastened in a clamped manner by means of casting compound 12, wherein a
translatory expansion of rail 9 is made possible by means of thin adhesive
layer 10 without creating forces which could cause measurement errors
acting on housing 1. These translatory movements are compensated in
adhesive layer 10.
To make the fastening of FIG. 4 even more free of compulsive forces and
more flexible in the linear direction, sliding layer 18 is provided
between adhesive layer 10 and casting compound 12, as seen in FIG. 5.
Sliding layer 18 can be a Teflon foil or an oil-containing paper. It is
particularly advantageous to employ an adhesive foil wherein the
protective paper is used as the sliding layer. Sliding layer 18 can also
be provided in place of or additionally between adhesive layer 10 and the
lateral surface of groove 11 or lateral surface of rail 9 of FIG. 5.
As seen in FIG. 6, rail 9 is fixed in place on the bottom and on one
lateral surface of groove 11 by means of adhesive layer 10. The further
lateral surface of rail 9 is also provided with adhesive layer 10 and
sliding layer 18. Clamping of rail 9 in groove 11 takes place by inserting
a rigidly or inelastically curing casting compound 12 into the free space
between sliding layer 18 and the further lateral surface of groove 11.
In accordance with FIG. 7, rail 9 rests slidingly on the bottom and one
lateral face of groove 11. The further lateral surface of rail 9 is
provided with an adhesive foil consisting of adhesive layer 10 and sliding
layer 18. Casting compound 12 is inserted between sliding layer 18 and the
further lateral surface of groove 11.
Fastening of rail 9 of FIG. 8 is similar to that of FIG. 4. Rectangular
groove 11 is provided in place of the dovetail-shaped groove 11 of FIG. 4.
Furthermore, sealing elements 21 are positioned to cover the gap so that
casting compound 12 is protected against environmental effects.
In the examples up to now the separating layer was provided in the form of
adhesive layer 10, or adhesive layer 10 plus sliding layer 18, between one
surface of rail 9 and casting compound 12. As shown in FIG. 9, separating
layers 10, 18 can also be located between casting compound 12 and a
lateral surface of housing groove 11. To further increase the translatory
mobility it is possible to also provide separating layers between rail 9
and casting compound 12 and additionally between casting compound 12 and
housing groove 11. The separating layer may be comprised solely of
adhesive layer 10 or sliding layer 18 or comprise adhesive layer 10 and
sliding layer 18 in combination.
FIG. 10 shows that the fastening between housing 1 and rail 9 is also
possible exclusively by means of adhesive layer 10. Linear expansions
between housing 1 and rail 9 and therefore also between housing 1 and
carriage 5 can be compensated by means of the inherent flexibility of
adhesive layer 10.
To further simplify mounting of rail 9, rail 9 of FIG. 11 extends out of
housing 1 at least in the areas intended for its fastening with carriage
5. Bores are provided in these areas, through which rail 9 can be rigidly
screwed to carriage 5 by the user. A dovetail-shaped projection of rail 9
itself interlockingly engages a groove 11 of housing 1. In accordance with
the invention, a highly elastic thin adhesive layer 10 is provided between
the inner surfaces of groove 11 and the surfaces of rail 9. The remaining
space may be filled with casting compound 12 and/or sliding layer 18 as
described in FIGS. 2 to 9.
If, for easier manipulation the width of rail 9 is selected to be less, it
is advantageous that housing 1 is additionally supported in a support area
A. This exemplary embodiment is represented in FIG. 12. As in FIG. 11, a
dovetail-shaped projection of rail 9 interlockingly engages groove 11 of
housing 1. A highly elastic thin adhesive layer 10 is provided between the
inner surfaces of groove 11 and the surfaces of rail 9. The remaining
space may be filled with casting compound 12 and/or sliding layer 18 as
described in FIGS. 2 to 9. One embodiment of the support area A is shown
in detail in FIGS. 2 and 3.
FIG. 13 shows an example of how an interlocking fastening between housing 1
and carriage 5 can be realized without the use of casting compound 12.
Housing 1 has a dovetail-shaped projection 21 extending in the measuring
direction X. Two rails 9.1 and 9.2 interlockingly engage both long sides
of projection 21. Rafts 9.1 and 9.2 are rigidly fastened on carriage 5 via
screws, while elastic adhesive layer 10 is provided between the surfaces
of projection 21 of housing 1 and the surfaces of rails 9.1 and 9.2 for
the translatory seating of housing 1. It is possible to provide a space or
a further adhesive layer 10 to prevent friction between the surface of
projection 21 facing carriage 5 and carriage 5 itself. It can be seen from
the examples that a simple and space-saving mounting is made possible by
the use of a long continuous fastening rail 9 and integrating it into
housing 1.
As illustrated in FIG. 14, it is also possible to replace the integrated
rail of FIGS. 1-13 with a rail 9.3 which is connected longitudinally
displaceable with respect to a further rail 9.4 on housing 1. Rail 9.3 is
fastened rigidly to carriage 5 and rail 9.4 rigidly to housing 1, for
example by screwing. An elastic adhesive layer 10 is shown as an example
of a connection, elastic in the long measuring direction X, between the
one rail 9.3 and the other rail 9.4. It is of course also possible for the
already described layers and layer combinations as well as shapes of
groove 11 to be used here as shown in FIGS. 2-10.
The embodiment of FIG. 14 has the advantage that linear measuring devices
already in use can be retrofitted in a particularly simple manner. Because
rail 9.4 is rigidly fastened on housing 1, when installed it is also an
integral part of housing 1.
It is also within the scope of the invention to use individual pieces of
rail separated from each other and embodied and fastened in accordance
with the above described examples in place of rails 9, 9.1, 9.2, 9.3, 9.4
extending over the entire measuring length. Thus, there will be a
plurality of rails or fastening elements which extend in the measuring
direction which are spaced apart from each other. An example thereof is
shown in FIGS. 17 and 18, wherein FIG. 18 illustrates a cross section of
the linear measuring device of FIG. 17. Fastening of the linear measuring
device takes place at both ends by means of one end piece 22 each. Groove
11 is cut into the face of end piece 22 facing carriage 5, into which
fastening element 9.5 has been interlockingly glued. Fastening of
fastening element 9.5 in end piece 22 may take place in the same way
fastening of rail 9 in housing 1 was disclosed with respect to any of the
embodiments shown in FIGS. 2-10. A translatory seating, free of force, of
housing 1 in relation to fastening elements 9.5 rigidly fastened on
carriage 5 is assured by the interposition of elastic adhesive layer 10
between fastening element 9.5 and end piece 22.
As shown in FIGS. 15 and 16, end pieces 23 can also be embodied in such a
way that they can be directly fastened on carriage 5 via elastic adhesive
layer 10. Elastic adhesive layer 10 is placed on one or more support areas
of carriage 5 where housing 1 is supported on adhesive layer 10 at the
support areas. As seen in FIG. 15, elastic adhesive layer 10 is positioned
between each end piece 23 and carriage 5. Housing 1 is additionally
rigidly fixed at approximately the center onto carriage 5.
To assure a translatory seating, free of force and friction-resistant, of
housing 1, it is possible to fasten housing 1 itself via elastic adhesive
layer 10 on carriage 5. In accordance with FIGS. 19 to 22, adhesive layer
10 has been directly applied to a surface of housing 1 for this purpose.
The central fixation in place can be omitted, because with the elastic
fastening the point of fixation is necessarily located in the center.
Additional guide elements 24 can be provided for lateral guidance. Elastic
adhesive layer 10 has also been inserted between guide elements 24 and
housing 1 to prevent friction and lateral play.
Adhesive layers 10 need not be applied over the entire surface, in
particular they can be provided in the form of strips spaced apart in the
measuring direction. Adhesive layer 10 also remains highly elastic after
drying, i.e. it is permanently elastic. When using casting compound 12, it
must be assured that in every case adhesive layer 10 is more elastic than
casting compound 12.
In a manner not illustrated, the invention can also be employed with open
linear measuring devices. In this case, measuring representation 2 is then
supported by a rail-shaped support body instead of housing 1.
The invention can also be realized if the groove is provided or placed in
the rail or the rail pieces, with a corresponding projection on the
housing.
With all embodiments in accordance with the invention the adhesive surface
of the housing and/or the adhesive surface of the fastening elements can
have indentations in accordance with German Patent Disclosure DE 89 11 313
U1. The indentations can also be embodied such that the adhesive layer
interlockingly fills or encloses an undercut of a groove or a projection
to prevent its detachment, as explained in European Patent Publication EP
0 465 966 A2, to whose contents express reference is made.
The invention may be embodied in other forms than those specifically
disclosed herein without departing from its spirit or essential
characteristics. The described embodiments are to be considered in all
respects only as illustrative and not restrictive, and the scope of the
invention is commensurate with the appended claims rather than the
foregoing description.
Top